The National Institute on Aging (NIA) supports through contracts several colonies of aged rats and mice for use in research on aging. Some investigators do not need live animals, but simp Iy collect specific tissue from the animals for their experiments. The purpose of this project is to provide a source of fresh-frozen tissue, suitable for multiple experimental protocols, from the NIA colonies of aged rats and mice. This will allow multiple investigators to make use of different tissues from the same animals, and will lower the cost of tissue for those investigators.